1. Field of the Invention
The invention relates generally to flow control devices for establishing temporary obstructions within a tubing string. In certain aspects, the invention also relates to devices and methods for pressure testing of production tubing within a hydrocarbon production well or for operating hydraulic tools within a tubing string.
2. Description of the Related Art
After a production well is drilled, cased, and, if required perforated, a string of production tubing is run into the cased wellbore. Hydrocarbons from a downhole formation are then drawn into the production tubing, under impetus of a surface-based pump, and brought to the surface of the well. After the production tubing is run into the wellbore, it is desirable to test the pressure integrity of the tubing before drawing production fluid from the formation. Leaks in the production tubing string result in inefficient production and can be costly to repair after production has begun.
In order to pressure test the production tubing, it is necessary to create a temporary plug or obstruction within the tubing string. Fluid is then introduced above the obstruction and pressurized so that any leakage can be detected. After testing, the obstruction must be removed from the tubing string. In other instances, it may be desirable to establish a temporary obstruction within the tubing string in order to actuate a hydraulic tool within the tubing string above the obstruction.
Unfortunately, current temporary plug flow control devices are problematic or less than reliable in practice. U.S. Pat. No. 5,996,696 issued to Jeffree et al. describes a rupture disk arrangement wherein a rupture disk, typically formed of nickel, is incorporated into the tubing string prior to running the tubing string into the wellbore. This type of device is also known commercially as a “well test membrane.” This arrangement is unsatisfactory for some purposes since it does not allow passage of fluid or tools through the tubing string while the tubing string is being tripped into the wellbore. The intact rupture disk prevents such passage.
The Model E Hydro Trip pressure sub, by Baker Oil Tools, is another flow control device that is used to establish a temporary blockage within a tubing string. This device uses collet fingers to provide a restricted-diameter ball seat upon which a plugging ball is seated to establish a fluid blockage. Upon the application of a predetermined amount of pressure within the tubing string above the plugging ball, several shear screws are sheared, permitting a sleeve within the tubing string to slide downwardly within the flowbore so that the collet fingers can retract back into a matching recess in the flowbore wall, thereby allowing the plugging ball to fall into the well sump below and result in an unplugged condition. This device may malfunction if the shear screws do not shear at the intended fluid pressure, or do not all shear at the same time, thereby causing the sliding sleeve to become stuck or to slide prematurely. In addition, this arrangement can only be used a single time. Once the shear screws have been sheared, no other plugging ball will be supported upon the ball seat unless the tubing string is first removed from the wellbore and then reset. This, of course, is costly and time consuming.
Also known is a shear-out ball seat sub that provides a temporary blockage of a portion of the tubing string when a ball-shaped plug is dropped into a tubing string and then seated upon a seating arrangement that is provided by a frangible member. The blockage is later removed by shearing away a frangible member to allow the plug to drop into the well sump. Unfortunately, this type of arrangement can only be located at the lower end of the tubing string and no other points along the tubing string, thereby limiting its usefulness. This arrangement, of course, is also limited to a single use.
The present invention addresses the problems of the prior art.